A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless networks, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs). Over the years, enhancements to LTE systems are considered by the third Generation Partnership Project (3GPP) so that an LTE Advanced (LTE-A) system can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard.
Multimedia Broadcast and Multicast Service (MBMS) is a broadcasting service offered via existing GSM and UMTS cellular networks. Recently, evolved MBMS (e-MBMS) has been introduced in the LTE specification for broadcasting or multicasting TV, films, and other information such as overnight transmission of newspapers in a digital form. To facilitate MBMS in LTE systems, a multicast control channel (MCCH) is used for the transmission of MBMS control information in each MBMS Single Frequency Network (MBSFN) area, and a multicast traffic channel (MTCH) is used for the transmission of user traffic to UEs receiving MBMS data packets. MBMS has the major benefit that the network infrastructure already exists for mobile network operators and that deployment can be cost effective compared with building a new network for the service. The broadcast capability enables to reach unlimited number of users with constant network load. The broadcast capability also enables the possibility to broadcast information simultaneously to many cellular subscribers, such as emergency alerts.
Push-to-talk (PTT) is a type of group communication method of having conversations or talking on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode. Push to Talk over Cellular (PoC) is a service option for a cellular network to offer mobile subscribers a walkie-talkie type of group communication with unlimited range. A significant advantage of PoC/PTT is the ability for a single mobile user to reach an active talk group with a single button press. The mobile user needs not to make several telephone calls to coordinate the communication group. PoC/PTT has been commonly based on 2.5G or 3G packet-switched networks and uses, for example, SIP and RTP/RTCP protocols. The Open Mobile Alliance (OMA) PoC specifies a PoC server for user management to enable PoC, based on VoIP and relied on IP multimedia Subsystem (IMS) as a service enabler.
PoC downlink (DL) traffic can be very bursty. In case of a group call, one talks and multiple users listen. Current PoC service realizes one-to-many communication via multi-unicasting. The traffic from one speaker is duplicated for the same number of times as the number of total recipients, i.e., many DL transmissions in response to one UL transmission. For large group size, bursty traffic can cause congestion in the core network. If the number of UEs of a group residing in a cell is big, then bursty traffic can cause network capacity to drop. Furthermore, the current SIP-based PoC service requires long call setup time. With SIP compression, call setup delay can be reduced to ˜1-2 s level. However, such setup delay is still longer than the <300 ms level recommended for public safety applications.
Therefore, it is beneficial to have more efficient data distribution scheme to ease the loading in the core network, and to have more efficient resource utilization to ease the bursty requirement of radio resource. PoC DL traffic multicasting is used to indicate the general idea of multicast distribution of the PoC DL traffic in the core network, in RAN, or in both the core network and RAN. With PoC DL traffic multicasting, mulitiple UEs can receive PoC DL traffic from the same physical transmission. Within the core network, the same packet is addressed to multiple eNBs via multicast address (PoC DL traffic multicasting in the core network). For efficient radio transmission, multiple UEs can monitor the same DL assignment in RAN (PoC DL traffic multicasting in RAN). It is also beneficial to enable idle mode PoC DL traffic reception from power saving and call setup latency perspectives.
Another important feature of a mobile wireless system such as LTE is the support for seamless mobility across eNBs and the entire network. Fast and seamless handover (HO) is particularly important for delay-sensitive services such as PoC. For traffic multicasting, PoC group mobility management is required in the core network so that PoC packet can be properly routed to relevant eNBs. For example, UE position to the granularity of cell is required. Otherwise, PoC multicast bearer cannot be handed over to a new target cell.
In the present invention, it is proposed to utilize MBMS in LTE/LTE-A systems to support PoC DL traffic multicasting, to enable efficient radio resource transmission, to reduce call setup latency via idle mode reception, and to provide PoC group mobility management to maintain PoC service continuity.